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Standard Computer Crypto ITA-2 →
ITA-5, commonly referred to as ASCII, is a 7-level (later: 8-level)
binary character-encoding scheme, derived from the older 5-level
ITA2 standard
(also known as Murray code or
Baudot).
ASCII is the abbreviation of
American Standard Code for Information Interchange.
The standard defines the 128 codes that can be made with 7 bits, all based
on the English (Latin) alphabet. As there are variations between
different countries, the common standard is known as US-ASCII.
Compared to the 5-level ITA2 standard (Baudot-Murray),
where the characters are
sorted in such a way that they cause minimum (mechanical)
stress on the equipment, characters in the ASCII
table are sorted in the logical order of the alphabet. The first ASCII
standard was published in 1963, with a major revision in 1967.
The most recent update was published in 1986.
ASCII is commonly used by computers
for storing programs (software)
and information (data). It has also been the major encoding scheme on the
internet, until it was surpassed by UTF-8 in 2007.
The initial ASCII standard was published when the first computers
entered the stage. These computers used 7-level punched paper tape for
storing their programs and the holes (b0-b6) were punched according to the
ASCII scheme. Later, when data was stored in the more convenient 8-bit
pattern, 8-level punched tape was introduced. It allows 256 characters,
of which the first 128 are defined by the ASCII standard. The extra bit
allows the introduction of a parity bit (P) – used for error checking –
but can also be used for adding 128 additional characters (b7).
Many different encoding schemes for 8-bit exist, but the majority of them
uses ASCII to define the lower 128 characters. The upper half
(sometimes referred to as the 'top-bit-set characters') are often used
for language-dependent encodings, such as ISO-8859-1 (Latin1) and
its Microsoft variant Windows-1252.
The definition of the lower 128 ASCII characters
is given below.
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Hex
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0
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1
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2
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3
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4
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5
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6
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7
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8
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9
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A
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B
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C
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D
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E
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F
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0
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NUL
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SOH
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STX
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ETX
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EOT
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ENQ
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ACK
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BEL
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BS
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HT
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LF
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VT
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FF
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CR
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SO
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SI
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1
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DLE
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DC1
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DC2
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DC3
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DC4
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NAK
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SYN
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ETB
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CAN
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EM
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SUB
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ESC
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FS
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GS
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RS
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US
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2
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SP
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!
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"
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#
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$
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%
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&
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'
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(
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)
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*
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+
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,
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-
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.
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/
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3
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0
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1
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2
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3
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4
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5
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6
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7
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8
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9
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:
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;
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<
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=
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>
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?
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4
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@
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A
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B
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C
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D
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E
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F
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G
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H
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I
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J
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K
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L
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M
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N
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O
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5
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P
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Q
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R
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S
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T
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U
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V
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W
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X
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Y
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Z
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[
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\
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]
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^
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_
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6
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`
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a
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b
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c
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d
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e
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f
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g
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h
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i
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j
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k
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l
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m
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n
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o
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7
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p
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q
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r
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s
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t
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u
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v
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w
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x
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y
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z
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{
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}
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~
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DEL
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The first 32 characters are unprintable. They are known as the control
characters and are mainly used for text formatting on teleprinters and
on the first generations of video terminals. Character 127 is also a
special code. It is used to delete a character which, in 7-level paper
tape, was done by punching 7 holes. Control characters are often
written as ^@ (NUL), ^A (SOH), ^B (STX), etc.
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#
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Hex
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Binary
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Char
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Name
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Description
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0
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00
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0000 0000
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^@
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NUL
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Null character (nothing)
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1
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01
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0000 0001
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^A
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SOH
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Start of header
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2
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02
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0000 0010
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^B
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STX
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Start of text
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3
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03
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0000 0011
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^C
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ETX
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End of text
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4
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04
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0000 0100
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^D
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EOT
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End of transmission
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5
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05
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0000 0101
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^E
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ENQ
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Enquiry
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6
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06
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0000 0110
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^F
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ACK
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Acknowlegment
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7
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07
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0000 0111
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^G
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BEL
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Bell (acoustic signal)
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8
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08
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0000 1000
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^H
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BS
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Backspace
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9
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09
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0000 1001
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^I
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HT
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Horizontal Tab
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10
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0A
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0000 1010
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^J
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LF
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Line feed
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11
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0B
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0000 1011
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^K
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VT
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Vertical Tab
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12
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0C
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0000 1100
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^L
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FF
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Form feed (clear screen)
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13
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0D
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0000 1101
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^M
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CR
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Carriage return (enter)
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14
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0E
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0000 1110
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^N
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SO
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Shift Out
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15
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0F
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0000 1111
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^O
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SI
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Shift In
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16
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10
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0001 0000
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^P
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DLE
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Data Link Escape
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17
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11
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0001 0001
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^Q
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DC1
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Device Control 1 (XON)
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18
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12
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0001 0010
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^R
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DC2
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Device Control 2
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19
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13
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0001 0011
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^S
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DC3
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Device Control 3 (XOFF)
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20
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14
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00010100
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^T
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DC4
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Device Control 4
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21
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15
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0001 0101
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^U
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NAK
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Negative Acknowledgment
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22
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16
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0001 0110
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^V
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SYN
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Synchronous idle
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23
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17
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0001 0111
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^W
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ETB
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End of Transmission Block
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24
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18
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0001 1000
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^X
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CAN
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Cancel
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25
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19
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0001 1001
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^Y
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EM
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End of Medium
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26
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1A
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0001 1010
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^Z
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SUB
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Substitute (also: End of File, EOF)
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27
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1B
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0001 1011
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^[
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ESC
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Escape
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28
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1C
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0001 1100
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^\
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FS
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File Separator
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29
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1D
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0001 1101
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^]
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GS
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Group Separator
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30
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1E
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0001 1110
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^^
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RS
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Record Separator
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31
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1F
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0001 1111
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^_
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US
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Unit Separator
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32
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20
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0010 0000
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SP
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SPACE character (printable)
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33
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21
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0010 0001
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!
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Exclamation mark (pling)
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34
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22
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0010 0010
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"
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Quote
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35
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23
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0010 0011
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#
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Hash
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36
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24
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0010 0100
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$
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Dollar
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37
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25
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0010 0101
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%
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Percent
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38
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26
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0010 0110
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&
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Ampersand
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39
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27
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0010 0111
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'
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Apostrophy
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40
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28
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0010 1000
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(
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Left bracket
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41
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29
|
0010 1001
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)
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Right bracket
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42
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2A
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0010 1010
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*
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Star
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43
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2B
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0010 1011
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+
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Plus
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44
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2C
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0010 1100
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,
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Comma
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45
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2D
|
0010 1101
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-
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Minus
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46
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2E
|
0010 1110
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.
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Full stop, point
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47
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2F
|
0010 1111
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/
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Slash, forward slash
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48
|
30
|
0011 0000
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0
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Zero
|
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49
|
31
|
0011 0001
|
1
|
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One
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···
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127
|
7F
|
0111 1111
|
^?
|
DEL
|
Delete
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Traditionally, in teleprinter jargon, the least significant bit (lsb) is called
channel 1 (c1), whilst the highest bit is channel 7 (c7) or, in the case of
8-bit ASCII, channel 8 (c8). This numbering scheme stems from
the telegraph era in which the five channels of the paper tape were numbered
1 to 5.
In the digital world however, it is more common to start numbering from 0 onwards, which is why in computer jargon, the bits of an 8-bit word
(i.e. a byte) are commonly referred to as b0 to b7.
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© Crypto Museum. Created: Thursday 21 May 2015. Last changed: Tuesday, 28 February 2023 - 07:55 CET.
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